One band member Heidi Herber said that they had no idea Biebz was even in the building when he asked if he could take a turn on the drums! She said:

"He came up and asked if he could play them. He just looked like a normal kid in the bar, except for the hat and hoodie. We had no idea [he was going to be there], in fact, he was one of the first people in bar."

According to sources, Bieberoni was playing an arcade game when someone spotted him — and things got expectedly crazy after that! She added:

Zayn previewed the duet by posting a black and white pic of himself with Swifty on his Instagram -- but hey, she is bestiez with his girlfriend Gigi Hadid, so it wouldn't be unusual that they hang out... But collab?!